​Contributed by Sian Kou-Giesbrecht, ​PhD student at Columbia University

Human activities increase the amount of nitrogen released into the atmosphere and subsequently increase atmospheric nitrogen deposition. Increased atmospheric nitrogen deposition in ecosystems can induce species loss through multiple mechanisms including increased competition and soil acidification. To better understand the impact of nitrogen deposition on plant species diversity across the continental US, data collected by the EPA, USGS, USDA was used to analyze nitrogen deposition, soil conditions, climate conditions, vegetation types and biodiversity of 15,136 forest, woodland, shrubland, and grassland sites and 3,852 herbaceous species.

Across a broad range of environmental factors, including vegetation types, soil conditions, and climate conditions, the study found that 24% of the sites examined are facing biodiversity loss due to increased nitrogen deposition. Moreover, the study found that some ecosystems are more vulnerable to nitrogen deposition than others. For instance, ecosystems with acidic soils or with open vegetation (grasslands, shrublands, and woodlands) showed greater vulnerability to nitrogen deposition than ecosystems with less acidic soil or with closed-canopy forest vegetation.

This result suggests that increased human-caused inputs of nitrogen into natural ecosystems are negatively affecting biodiversity in many ecosystems across the continental US, and it also suggests that atmospheric nitrogen deposition should be taken into account when establishing air quality standards.